Ozone as a powerful and clean oxidizing agent has been attracting increased attention. The use of ozone particularly for water treatment has been increasing since treatment with ozone is advantageous, for example, in that because the product of ozone decomposition is oxygen, ozone-treated water is not caused to contain any residual substance, unlike conventional chlorine-treated water, and in that the decomposition rate of ozone is so high that ozone itself does not remain in the treated water; hence, there are no problems of secondary pollution. For producing ozone which is a useful oxidizing agent as described above, electrical discharge methods and electrolytic methods have mainly been employed conventionally. At present, however, the electrolytic methods are most typically employed, because of the advantages of product purity and ease of operations.
The above advantages are brought about because the electrolytic ozone generators (electrolytic ozonizers) used in the electrolytic methods employ as the anode a lead oxide-based electrode performing an excellent ozone-evolving function. Due to such ozonizers, ozone can be obtained at high concentrations by conducting procedures almost the same as those in ordinary water electrolysis. In such ozone generators, pure water (ion-exchanged water) is used as the raw material and a perfluorocarbon sulfonic acid-based ion-exchange membrane is mainly used as a solid electrolyte, in combination with lead dioxide as the anode, to generate ozone. By this method, oxygen containing ozone gas at a concentration of about 15% can be obtained. The thus-produced ozone-containing oxygen may be used as it is or after being dissolved in water to give ozone-containing water. This electrolytic method is advantageous in that the apparatus has a simple structure and its operation is simple. Hence, attention is now focused on this apparatus, among small-sized ozonizers producing small amounts of ozone, which is regarded as an ozone generator that generates ozone at a high concentration.
However, this ozone generator with excellent performance has some drawbacks. The most serious of these is that high-purity pure water (or ion-exchanged water) should be fed to the ozone generator in order to protect its ion-exchange membrane; the pure water should be regulated so as to have an electrical conductivity of 1 .mu.S/cm or less if possible, and 10 .mu.S/cm or less at the worst. For maintaining such an electrical conductivity, the ozone generator is equipped with an ion-exchange column packed with an ion-exchange resin before the electrolytic cell, and the feed water is allowed to pass through the ion-exchange column, where impurities are removed from the water, and the resulting water is then fed to the electrolytic cell.
The anolyte in the electrolytic cell, however, decreases in amount not only by consumption through electrolysis but also when part of the anolyte penetrates as migrant water through the ion-exchange membrane from the anode side to the cathode side together with positive ions. In the case of ordinary perfluorocarbon sulfonic acid-based ion-exchange membranes, the number of such migrant water molecules is from 2 to 2.5 per positive ion, such a migrant water amount being significantly large because it is four- to five-fold larger than the amount of water which undergoes electrolysis. Because of the above, a large quantity of pure water is fed to the electrolytic cell normally by using a relatively large-sized ion-exchange column. However, this conventional method involves problems in terms of cost and equipment construction, because the migrant pure water is discarded and because of the necessity of use of a large-sized ion-exchange column and of replacement of the ion-exchange resin with fresh one at short intervals. These problems constitute obstacles particularly to easy maintenance of the apparatus.